In recent years there has been a recognized and, therefore, growing need to accommodate the needs of those in wheelchairs on public transportation. To this end, there has been a large number of devices proposed to provide wheelchair lifts in transit buses--those intended for use on city and suburban streets. Such buses have two features that have shaped the design and location of such lifts on the bus. One is that they are typically not far off the ground or pavement and the other is that they usually have more than one door. Therefore, it has been possible to design wheelchair lifts to be mounted inside one of the doors leaving at least one other door unencumbered. Likewise, because the distances between pavement or curb level and the bus floor level are not excessive, the actuating or raising and lowering means can be mounted adjacent a doorway stairwell and still leave room for the steps and floor space in the vicinity of the steps.
Tour or intercity buses, however, have totally different problems. They are, first of all, much taller than transit buses. In a typical tour bus, the floor of the bus may be 54 inches above the pavement, while the underside of the bus may be 13 inches above the pavement. Similarly, the floor of a railway car may oftentimes be many feet above the floor of an adjacent platform. These distances require a lifting mechanism that cannot easily be contained within the spaces available around the stairwell of such a bus or railway car.
Although the lift disclosed in U.S. Pat. No. 07/528,744 (the '"744 application") functions highly effectively and is a significant improvement over prior lift designs, it has been determined that under certain conditions the carriage assembly which supports the lift platform has a tendency to inadvertently move in the direction of deployment along the support rails on which the carriage is slidably mounted. More specifically, when in the stowed position, the platform assembly may move outwardly toward the door closing off the compartment in which the lift is housed. Such movement, which typically occurs as a result of hydraulic seepage of the hydraulic actuators which cause the carriage to move back and forth along the support rails, may result in damage to the associated compartment door, or to the lift itself.
To avoid this problem, wheelchair lifts similar to the lift of the present invention have used a mechanical latch assembly for securing the lift platform in the stowed position. One such mechanical latch assembly includes a hydraulic cylinder provided solely for the purpose of causing the latch to move from a locked to an unlocked position. Because the addition of such a hydraulic cylinder, and its associated hoses and controls, adds to the cost and complexity of the lift, a need exists for an effective mechanical stow latch which does not include a hydraulic cylinder provided solely for the purpose of actuating the latch.
With lifts of the type disclosed in the '744 application, during certain operational phases of the lift the possibility exists that someone could fall out of the door opening positioned above the lift onto the ground or onto the lift itself. Thus, a need exists for a system which reduces or avoids the possibility of such a fall.